The present invention relates to a display device driven by a small amount of power, and more particularly to a low-power driven electronic display device, which is a combination of a solar cell and a liquid crystal device, not requiring recharging and a method for controlling it.
There have been proposed many display devices powered by a power supply using a solar cell or the like. For example, JP-A-2001-184033 discloses a display device which has a display area formed of a solar cell and a liquid crystal material having a memory property and does not need power for displaying. JP-A-5-73117 discloses a technology which connects a power buffer for storing electric power between a solar cell and a display device to drive a display circuit.
A display device having a solar cell as its power supply has a considerable change in supplied electric power depending on an amount of light radiated to the solar cell. Then, when the electric power becomes insufficient, a display cannot be driven, and the display disappears. Therefore, it has been general to add an auxiliary power supply unit for compensation of the power to make it possible to perform the display drive by combining the solar cell with a rechargeable secondary battery even if the solar cell output stops. JP-A-2000-112441 discloses a drive method by which an illumination sensor for detecting an amount of light incident on the solar cell is disposed to reduce power consumption by limiting the power of a backlight for adjusting display luminance when peripheral illumination is high. In recent years, an organic solar cell using a high-molecular or low-molecular organic film is attracting attention as a lightweight and thin unit for realizing a high power capacity. This type of organic solar cell is described in detail in a paper by A. Konno entitled “Present and future of organic solar cell” “Applied Physics” Vol. 71, No. 4 (pp 425 to 428) issued by Japan Society of Applied Physics Association, Apr. 10, 2002.